JP2722938B2 - Organic composite zinc-coated steel sheet for exterior - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite zinc-coated steel sheet having an excellent electrodeposition coating property and used for an exterior surface of an exterior.

[0002]

2. Description of the Related Art In recent years, an organic composite zinc-based coated steel sheet exhibiting excellent corrosion resistance has been developed and applied to an inner plate material for perforated corrosion of automobiles, etc., and has greatly improved the service life thereof. .

[0003] The "organic composite zinc-based plated steel sheet"
A rust-preventive steel sheet having a multilayer structure comprising a zinc-based plating (Zn or Zn alloy plating) film as a first layer, a chromate film as a second layer, and an organic resin-based film as a third layer on a steel sheet surface. In recent years, there has been a movement to apply organic composite zinc-based steel sheets to exterior surfaces of automobiles, etc., with the aim of further improving the rust resistance of exterior surfaces (for example, the rust resistance of impact parts of splashed pebbles). (Japanese Patent Laid-Open No. 64-78832)
Reference).

However, an organic composite zinc-coated steel sheet is
Originally developed as an inner plate material for automobiles,
Although excellent in cratering resistance at the time of cationic electrodeposition coating, when used as an exterior material, it is unique to "press press flaw inspection part by grinding with a grinding wheel after press molding" or "grinder polishing of press flaw part" There was a problem in the electrodeposition coating finish of the damaged part of the organic composite film on the surface such as the "care part". In other words, it is pointed out that the presence of the damaged portion of the organic composite film as described above appears as unevenness of the coating film at the time of electrodeposition coating, which remains after the inner and upper coatings, thereby significantly deteriorating the appearance quality as an automobile or the like. It was being done.

[0005] In view of the above, the object of the present invention is to obtain a uniform and beautiful electrodeposition finish even if a film damaged portion is present, and to have excellent rust prevention performance as it is. The objective was to realize an organic composite zinc-coated steel sheet.

[0006]

The present inventor has conducted research from various viewpoints to achieve the above object,
“Electrodeposition coating on an organic composite zinc-coated steel sheet after press forming is usually performed after applying zinc phosphate treatment after pressing. And after the zinc phosphate coating is formed on the exposed portion of the steel sheet surface, in this case, the electric resistance at the time of the maximum current flow when applying the cationic electrodeposition coating to the organic composite zinc-based plated steel sheet is “ A value in a specific range in terms of the equivalent electrical resistance of the surface of the electrodeposited coated material, for the same electrical resistance of "the surface of the underlying steel sheet treated with zinc phosphate" and "the first layer of zinc-based plating film treated with zinc phosphate". By controlling the composition and film thickness of the organic resin film as the third layer so as to achieve, it becomes possible to perform electrodeposition coating without damage on the appearance even if the film is damaged by surface polishing or grinding. " With new knowledge It could be.

The present invention has been completed by further study based on the above findings and the like. "A zinc-based plating film as a first layer, a chromate film as a second layer, and a third layer on a steel plate. From the “electrical resistance (R) at the time of the maximum current flow when performing cationic electrodeposition coating” on the “Zinc-based plated film as the first layer”. the conductive when the maximum current was supplied <br/> air resistance minus (R ₁₎ "in performing cationic electrodeposition coating against those subjected to zinc treatment (R-R _1), or The " R"
"The maximum current when performing cationic electrodeposition coating against those subjected to zinc phosphate treatment by energizing the serving base steel sheet from
(R−R ₂ ) obtained by subtracting the electrical resistance (R ₂ ) of the electrodeposited coating material from −650 to +1450 m in terms of the surface area of the object to be coated.
By was film structure formed by adjusting the range of Ω · cm ^2, and so uniform and beautiful electrodeposition coating finish appearance fully satisfactory for the exterior can be obtained as a film lesion was present The point "has a great feature.

[0008]

In other words, the present invention is based on the concept that, in the case of a conventional organic composite zinc-coated steel sheet, if a film damaged portion exists, the difference in electrical resistance between the film damaged portion and the undamaged portion during electrodeposition coating is large.
Therefore, the current concentrates on the portion where the electric resistance is small, and the electrodeposition film thickness in the portion becomes relatively thick, and the appearance becomes poor after electrodeposition. " By adopting the method described above, the electrodeposition coating property of the organic composite zinc-based plated steel sheet is improved.

Here, as a standard for calculating the electric resistance difference, “an organic composite zinc-based plated steel sheet, a zinc-based plated film as a first layer subjected to a zinc phosphate treatment, and a steel sheet as a base material subjected to a zinc phosphate treatment. The electrical resistance of the coating is limited to "when the maximum current is applied when applying cationic electrodeposition coating to the organic composite zinc-coated steel sheet." This is because the swelling is caused by the influence of, and the electric resistance is different from the dry state. In addition, as a standard for calculating the electric resistance difference, “a zinc-based plated film as a first layer” and “a steel sheet as a base material”, which are exposed at a damaged portion of the film and cause non-uniformity of electrodeposition coating property, are particularly phosphorous. The electrical resistance value of the zinc oxide treated product was specified because, as mentioned above, the zinc phosphate film is usually formed on the damaged portion of the film and is used for electrodeposition coating. This is because the zinc-based plating film surface and the base steel plate surface are covered with the zinc phosphate film at the time of electrodeposition coating. By the way,
As can be understood from the description, the “re
"It has been treated with zinc phosphate"
It means that it includes applying a zinc phosphate treatment
However, it is not possible to pass through the material to be treated for practical electrodeposition coating.
Zinc phosphate treatment under conditions that are always applied. "
Needless to say, it means.

In the cation electrodeposition coating, the resistance value [R] in terms of the surface area of the material to be electrodeposited at the time of the maximum energization is as follows: the electrodeposition voltage is V (V), the maximum current is I (A), and the electrodeposition voltage is I (A). If the surface area of the painted object is S (cm ² ), the formula Is the value calculated by

The electric resistance can be measured by measuring the voltage and current during energization during normal electrodeposition coating. For example, for a workpiece having a surface area of 420 cm ² , the distance between the workpiece and the electrode is set to 10 cm and the voltage is set to 32 cm.
Boom energized at 0V (through increase in Boom and maximum voltage at a time
The measurement results of a voltage and current in the case of electrodeposition) is shown in FIG. 1, the (1) formula "I" and "V" a in FIG. 1
R may be calculated by capturing the values as [I] and [V]. It should be noted that the measured V value naturally includes, for example, a voltage drop caused by the electrodeposition liquid. However, the present invention stipulates that the base (base material) steel sheet and the zinc-based plated steel sheet be phosphoric acid. Since there is a difference in electrical resistance from that after zinc treatment, there is no problem in actual measurement under the same electrodeposition conditions.

As described above, according to the present invention, the coating composition of the organic composite zinc-based coated steel sheet is adjusted so as to reduce the difference in electrical resistance between the damaged part and the non-damaged part at the time of electrodeposition coating. The uniformity of the current that flows sometimes is improved to improve the appearance of electrodeposition coating, and the suitability as an exterior material is improved. However, the value obtained by subtracting "the electrical resistance R ₁ of the material of the first layer galvanized and zinc phosphate treatment" to "the electrodeposition coating material the electrical resistance R in the (organic composite galvanized steel sheet)" (R -R ₁ ) or a value obtained by subtracting “electric resistance R _{2 of} a material obtained by treating a base steel sheet with zinc phosphate” from “the R” (R−
R ₂ ) is -650 m in terms of the surface area of the material to be coated.
Below the Omega · cm ^2, the electric resistance of the undamaged portion becomes larger than the film lesion, as coating unevenness after electrodeposition ChakumakuAtsu is thickened by electrodeposition coating of non-lesion for that reason coating damaged portion Because it stands out, it is unsuitable as an exterior material. On the other hand, if the above electric resistance difference exceeds +1450 mΩ · cm ² , the conductivity of the non-damaged portion is reduced, and intensive discharge occurs locally (pinhole-shaped microscopic film defect portion) during electrodeposition coating. This tends to increase the occurrence of cratering, making it unsuitable as an exterior material.

In the present invention, the coating composition of the organic composite zinc-based coated steel sheet is defined by the specific electrical resistance difference. As means, A) a method of controlling the thickness of the organic film as the third layer (usually about 1 μm); B) Addition of a hydrophilic resin or a hydrophilic group such as silica to be contained in the organic film as the third layer. And the method of controlling the amount of the substance to be added.

[0014] The chromate treatment carried out when producing an organic composite zinc-based plated steel sheet is a general reaction type chromate process, coating type chromate process or electrolytic chromate process, or Each chromatization treatment or the like which is carried out by adding silica to the treatment liquid used for these can be applied. In addition, as the organic film as the third layer of the organic composite zinc-based plated steel sheet, an epoxy-based resin, an acrylic-based resin, and a resin obtained by adding silica or a hydrophilic resin to the resin can be used.

Next, the present invention will be described more specifically with reference to examples.

[Example] First, Zn-13wt% Ni alloy plated steel sheet (basis weight:
30 g / m ² ) as a base, and “Cr / SiO ₂ = 1
/ 1, Cr / PO ₄ = 1/1 ”, and a coating-type chromate treatment was performed so that the Cr adhesion amount was 60 mg / m ² .

Subsequently, a) The urethane-modified epoxy-based clear (20% SiO ₂ added, 10% hydrophilic polyamide resin added) is used as an organic resin film on the chromate film to change the film thickness. (B) Acrylic resin-based clear (with 15% SiO ₂ added), the electrical resistance of which is controlled by changing the amount of hydrophilic polyamide resin added. By coating, an “organic composite zinc-based plated steel sheet” was manufactured.

Next, samples having the dimensions shown in FIG. 2 were collected from each of the obtained organic composite zinc-based plated steel sheets, and the electrodeposition coatability was examined. When investigating the electrodeposition coating property, a "film damaged portion" was formed on the sample using # 120 sand paper as shown in FIG. 2, and then the electrodeposition coating was performed in the process shown in FIG. The electrodeposition appearance was evaluated.

FIG. 4 shows the results of these investigations.
In FIG. 4, "electrical resistance difference" refers to "base steel sheet treated with zinc phosphate" or "Zn-Ni alloy plated steel sheet treated with zinc phosphate" and "organic coating formed. (That is, “organic composite zinc-based plated steel sheet”) ”, the larger absolute value of the difference was adopted.
The results of “Evaluation of appearance after electrodeposition coating” in FIG. 4 are indicated by “「: excellent, ○: good, Δ: poor, ×: extremely poor ”. From the results shown in FIG. 4, it can be confirmed that any of the organic composite zinc-based plated steel sheets according to the present invention has a sufficiently satisfactory cationic electrodeposition coating property as an exterior surface material.

[0019]

[Summary of Effects] As described above, according to the present invention, it is possible to realize an organic composite zinc-based alloy coated steel sheet exhibiting extremely excellent electrodeposition coating properties. Industrially useful effects such as application of a composite zinc-based alloy-plated steel sheet can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram regarding how to capture an electric resistance value (R) and a voltage value (V) during electrodeposition coating.

FIG. 2 is an explanatory diagram of a sample for investigating electrodeposition coating properties in an example.

FIG. 3 is an explanatory diagram relating to an electrodeposition coating property evaluation test procedure adopted in Examples.

FIG. 4 is a graph showing the results of an investigation of electrodeposition coating properties in Examples.

────────────────────────────────────────────────── (5) Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C23C 22/24 C23C 22/24 22/82 22/82 (56) References JP-A-63-35798 (JP, A) JP-A-3-170698 (JP, A) JP-A-3-56694 (JP, A) JP-A-60-50180 (JP, A) JP-A-60-174879 (JP, A) Edited by Shigeo Hiro and Keiichi Uchida, "Electro-Technical Library 21 Electrodeposition Coating" (Showa 44-12-30), published by Nikkan Kogyo Shimbun, p. 89

Claims (1)

(57) [Claims] An organic composite zinc-coated steel sheet comprising a steel sheet provided with a zinc-based plating film as a first layer, a chromate film as a second layer, and an organic resin-based film as a third layer,
From "Electrical resistance (R) at the time of applying the maximum current when performing cationic electrodeposition coating on this," perform "cationic electrodeposition coating on the zinc-based plating film as the first layer which has been subjected to zinc phosphate treatment. the maximum current electrical resistance when energized (R ₁₎ when "minus the (R-R _1), or the" to those subjected to zinc phosphate treatment serving base steel sheet "from" R When the above maximum current is applied when performing cationic electrodeposition coating
(R−R ₂ ) obtained by subtracting the electrical resistance (R ₂ ) of the electrodeposited coating from −650 to +1450 m in terms of the surface area of the material to be coated.
An organic composite zinc-coated steel sheet for exterior use, characterized by being adjusted to the range of Ω · cm ² .